The invention relates to an installation for the monitoring of message transmission systems with lightwave conductors with mutually directed message flow in the form of a four-wire transmission.
In message transmission on lightwave conductors, particularly with the use of laser transmitters, retinal damage can occur in observing the lightwave conductor ends. This can occur, for example, in that the end of a torn lightwave conductor cable is found by a non-expert and is investigated by him. The intensive light beam flowing from the lightwave conductor end, which is, however, usually invisible since it is infrared, can then cause damage to the eye.